1. Field of the Invention
The present invention relates to a dot printer. More specifically, the present invention relates to an improvement in such a dot printer as a wire dot printer for use in a slip issuing machine wherein character data is printed through depression of dot pins onto a print medium.
2. Description of the Prior Art
A conventional dot printer is structured to print characters to be printed by decomposing the same into a combination of dots. For example, a wire dot printer comprises a print head for dot printing including a plurality of dot pins arranged in one column, which is adapted such that the dot pins are driven in accordance with character data so that the tip ends of the corresponding dot pins are depressed onto a print medium while the print head is moved in the lateral direction. Such dot printer is usually adapted such that an ink ribbon is interposed between a print head and a print medium so that the portions of the print medium which are depressed by the dot pins become blotted with the ink of the ink ribbon, whereby the corresponding dots are printed. In the case where a so-called pressure sensitive coloring sheet is employed as a print medium, the portions of the print medium which are depressed by the dot pins become colored, whereby the dots are printed. In such a case, no ink ribbon is required as a matter of course.
In case where such a ink ribbon as described above is employed, an ink of the ink ribbon is dispersed due to depression by the dot pins, whereby dispersed ink could enter between the dot pins and a guide enclosing therearound. If and when a dot printer has not been used for a long period of time in such a situation, the ink between the dot pins and the guide solidifies, which makes it difficult for the dot pins to be driven smoothly. As a result, malfunction in printing is liable to occur, for example, the dots to be printed are not properly printed. Furthermore, in the case where such a pressure sensitive coloring sheet as described above is utilized, coloring powder coated on the surface of the pressure sensitive coloring sheet and a paper dust are dispersed due to depression by the dot pins and those adhere to the periphery of the dot pins. In such case as well, the adhering material around the dot pins solidify during a long period of time when the dot printer is not utilized, which makes it difficult for the dot pins to be smoothly moved. As a result, malfunction in printing becomes liable to occur.